The present invention relates to an adjustable depth truss for use in such applications as supporting a horizontal concrete form. More particularly, the present invention relates to an adjustable depth truss used in a flying table.
In the art of construction, a great variety of concrete forms are used. One common form is a horizontal deck form for pouring concrete flooring in multi-story buildings. To add another story to the building, a deck form is placed on top of the previously poured floor, and concrete is poured on top of the form to construct the next highest floor. These forms are usually called "flying tables", because, after the new floor has set, the form is lowered away from the new ceiling, transported to the edge of the building, and "flown" to the floor above to support another pour.
Normally, flying tables are constructed with a metal truss, the truss being supported by a jack stand or leg resting on a support surface such as the previously poured floor. To move the flying table, the truss is lowered on the jack and the entire form is moved on rollers to the edge of the building where it is picked up by a crane and flown to the next floor.
The trusses which form part of conventional flying tables suffer from a number of disadvantages and limitations which hamper their utility. First, because the depth of the truss is not adjustable, the height of the flying table above the support surface of previous pour is limited to the extent that the adjsutability of the jack stand or leg allow. Because the height variability of the flying table is limited to the range of the jack and/or leg, which is a relatively limited range, it is difficult to pour floors which are more than a certain height above the support surface or previous pour. Second, conventional flying tables are constructed of steel or aluminum to provide sufficient strength. However, the use of steel makes the flying tables relatively heavy, requiring either that they be broken into sections to be moved from one floor to another (i.e., handset) or that a very large crane be used to fly the entire form. Larger cranes are more expensive to operate than the smaller cranes and may be prohibited by space constraints. Of course, handset forms must be repeatedly assembled and disassembled, which is labor intensive and slow. Finally, metal flying tables are expensive.
Another limitation of known trusses is that they do not have any interchangeable components which would allow the use of those components on other forms or devices used in construction, such as scaffolds or gangforms. Further, they are available only in certain sizes and are not, therefore, easily adaptable for use in a particular situation. A significant savings in cost and reduction in inventory requirements would be realized if the components of the flying table could be interchanged with the components of other types of concrete forming, for instance, if the chords of the truss are interchangeable with the joists of a flying table or the studs and walers of a gangform. In addition to that cost saving, the ability to assemble and disassemble a truss into a desired size and length would add significant flexibility of use which would likewise result in a significant cost saving.
Aluminum trusses are available which help to overcome the weight problem, but they are much more expensive than steel trusses and do not have any components which are specifically designed to be interchangeable with the components of other forms. Further, the depth of those aluminum trusses is not adjustable, which limits their utility. One attempt to solve that problem is currently being marketed in the form of a double channel aluminum extrusion truss which is adjustable in only one mode. An extendable leg is bolted between the channels of the bottom chord of that truss stand and attached to two adjacent diagonals to take the place of the jack. However, this leg is for adjustment of the height of the truss and not the depth. The double channel chord member of that truss can be used as a waler, but the thin web of that member limits its bearing capacity thereby limiting its use in this matter such that it is not truly interchangeable with other components.
Using lumber trusses reduces the initial cost of the materials, especially when that cost is compared to the cost of aluminum. Further, lumber is relatively light in weight and can be handled by smaller cranes. However, lumber components are normally job-site constructed for each use by nailing the wood together. Nail joinery is not strong enough for heavy loads, which leads to the use of many more nails, which further damages the wood. Consequently, lumber trusses have a limited capacity for reuse.
It is, therefore, an object of the present invention to provide a light weight and low cost truss, capable of being assembled and disassembled repeatedly without damage, and having components which are interchangeable with the components of other concrete forms.
It is another object of the present invention to provide a truss which is capable of being conveniently adapted for use in a wide variety of applications, thereby reducing the number and types of truss components which must be kept in inventory by the contractor.
It is another object of the present invention to provide an adjustable depth truss.
Further, it is an object of the present invention to provide a truss which can be used as a component of a light weight flying table deck form.
Further, it is an object of the present invention to provide a flying table whose components can be used as components of other forms or devices for forming.
Further, it is an object of the present invention to lower the accessory inventory costs for contractors.
Further, it is an object of the present invention to employ accessories for assembly of flying tables which are identical to the accessories for assembly of gangforms and for scaffolds, such as connector hardware, hookrods and brackets.
Further, it is an object of the present invention to provide a truss of light weight to decrease the size of the crane necessary to fly a flying table.
These and other objects of the present invention will become evident to those skilled in the art who have the benefit of the description of the preferred embodiment which follows.